1. Field of the Invention
The present invention relates to an emergency draining device for pneumatic cylinders, which is intended to cause the stopping thereof and which comprises:
a pressurized fluid supply inlet which is connected directly or indirectly to a pneumatic distributor, PA0 a fluid outlet, which is connected to a chamber of the cylinder, PA0 and a control inlet, which receives a control signal acting on an internal switching means adapted to connect the fluid outlet to the atmosphere or not, the inlet and the outlet being in communication when this signal is absent.
2. Description of the Prior Art
Such devices may be used in all pneumatic installations, either for stopping the movement of the actuating rods of cylinders, for example when a danger occurs, or for making manual actuation of the rod of this cylinder possible, for carrying out a checking or adjusting operation.
Rapid draining circuits are already known for cylinders which, so as to obtain the above mentioned draining possibility, use a monostable 3/2 distributor; this 3/2 distributor is placed between a chamber of the cylinder and a normal pneumatic distributor so that, in the presence of a control signal, the chamber of the cylinder is connected to the distributor, whereas, in the absence of this signal, the chamber is connected to exhaust and so that the duct coming from the normal distributor is closed.
We cannot really speak here of a device specially adapted to the desired function to the extent that this 3/2 distributor is designed for more general functions and has a form adapted thereto.
The fitting and use of such a distributor has the disadvantage, on the one hand, of requiring much time and, on the other hand, in resulting in cumbersome assemblies. When the above mentioned fitting is finished, the presence of this 3/2 distributor in the vicinity of the cylinder is not appreciated by users to the extent that it results in a piling up of members which obviously have not been designed for this purpose.
Furthermore, the fitting of these 3/2 distributors, which is justified when speed regulators are associated with the cylinder, means that they are placed between the cylinders and said regulators. Because of the modern tendency to generalize the use of speed regulators incorporated in connections fitted directly to the cylinder body, the use of these 3/2 distributors for the above mentioned purposes has become obsolete.
The need to stop a cylinder instantly or to make it operable by hand is often met with in industrial installations where it is either indispensable to limit the damage and the risks which malfunctions may cause or it is necessary before starting up or after repairing.
A pneumatic cylinder can only be stopped and placed in a neutral position if the pressures which are exerted on the two faces of its piston disappear after decreasing simultaneously.
Since the cylinders are supplied from ducts which connect them to distributors and since these latter are themselves connected to a compressed air source, often a distance away, by a general line and to an exhaust manifold, it is sometimes difficult to rapidly empty or drain the cylinder by interrupting the inlet of fluid in the general line and draining this latter.
Such symmetrical draining is even longer and more difficult to obtain if, as is frequently the case, the air escapes from the cylinder to the distributor through one or more flow limiting means. In this latter case, it can be observed that, since the masses of compressed air contained on each side of the piston escape at different rates, they continue to exert on this piston different pressures which prolong the movement thereof after the pneumatic isolating switch has been opened.
It is also known that a 3/2 modular pneumatic isolating switch may be used for venting to the atmosphere a pressurized supply line serving a multiplicity of distributors, each associated with a respective cylinder; such an isolating switch, which at the same time interrupts the intake of pressurized fluid from the source in the general line and connects this latter to the atmosphere, is always placed at the head of this line, so that the delay in draining must be taken into account which is due to the line lengths, distributors and flow limiters mentioned above.